Wide angle camera lens system of retrofocus type

ABSTRACT

A wide angle camera lens system of retrofocus type comprising a forward lens system having a negative refractive power and consisting of first and second lens elements and a master lens system having positive refractive power and consisting of third and fourth lens elements and a backward lens system having positive refractive power and consisting fifth, sixth and seventh lens elements and giving negative refractive power to an air lens formed between the third and fourth lens elements in the master lens system.

OR 3,737,213 Q United States P Yamashita [54] WIDE ANGLE CAMERA LENS SYSTEM OF RETROFOCUS TYPE [75] Inventor: Nobuo Yamashita, Suwa, Tama City, Tokyo, Japan [73] Assignee: Olympus Optical Company Limited,

Tokyo, Japan [22] Filed: Feb. 2,1972

[2]] Appl. No.2 222,765

[52] U.S. Cl ..350/214 [5 l] Int. Cl. ..G02b 9/64 [58] Field of Search "350/214, 215

[56] References Cited UNITED STATES PATENTS 3,506,339 4/1970 Kazamaki ..350/2l4 3,737,213 June 5, 1973 3,512,874 5/1970 Waltche ..350/2l4 Primary Examiner.lohn K. Corbin Attorney-Eric H. Waters, John G. Schwartz and J. Harold Nissen 1 ABSTRACT A wide angle camera lens system of retrofocus type comprising a forward lens system having a negative refractive power and consisting of first and second lens elements and a master lens system having positive refractive power and consisting of third and fourth lens elements and a backward lens system having positive refractive power and consisting fifth, sixth and seventh lens elements and giving negative refractive power to an air lens formed between the third and fourth lens elements in the master lens system.

5 Claims, 20 Drawing Figures F/Gl3 perture efflc/kenc y 0.

lmage Hei m (38') PATENTED JUN 5 \975 aberratio WIDE ANGLE CAMERA LENS SYSTEM OF RETROFOCUS TYPE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide angle camera lens system of retrofocus type.

2. Description of the Prior Art Upon designing a lens system having a long back focus relative to a focal length, it has been a common practice to arrange a forward lens system having a negative refractive power and a backward lens system having a positive refractive power. In general, such a lens system is termed as a retrofocus type lens system. In this retrofocus type lens system, in order to obtain a long back focus, it is necessary either to increase the refractive power of the forward negative lens system or to increase the space between the forward and backward lens systems. However, in the former case, although it is convenient for making the lens system compact, it results in an increase of the coma, the spherical aberration, the negative distortion, etc. On the contrary, in the latter case, it is possible to compensate various aberrations, but a size of the lens system becomes large. Hitherto it has been considered that it is very difficult to obtain a compact lens system of the type mentioned above with highly compensated aberrations.

SUMMARY OF THE INVENTION The present invention has for its object to provide a novel wide angle camera lens system of retrofocus type having the following characteristics;

1. a relative aperture F of 3.5,

2. a wide angle of field up to 76,

3. a long back focus of about 1.35 f, wherein f is a composite focal length,

4. a compact construction, i.e. a small diameter of a front lens surface of a first lens element and a short axial length of the whole lens system,

5. a large amount of light at a periphery, and

6. a satisfactory correction of different aberrations.

An improved wide angle camera lens system according to the present invention comprises a first lens (L,) consisting of a positive lens element having a small refractive power, a second lens (L consisting of a negative meniscus lens element having a convex surface faced towards an object, a third lens (L consisting of a positive lens element, a fourth lens (L consisting of a positive meniscus lens element having a concave surface faced towards an object, a fifth lens (L consisting of a positive meniscus lens element, a sixth lens (L,,) consisting of a biconcave negative lens element and a seventh lens (L consisting of a biconvex positive lens element and satisfies the following conditions;

t,+r,,+t /d,+d, 0.8

0.4f d,+d, l.lf

l.2 r,/r-, 3.5, r 0, r-, 0

wherein, f designates a composite focal length,

t t t designate air spaces formed between two adjacent lens elements,

d,, d,, .d-, designate axial thicknesses of the lens elements, and

r r r designate radii of curvature of the lens surfaces.

According to the present invention, the inventor has succeeded in designing an improved wide angle camera lens system of retrofocus type by arranging a master lens system (L L having a positive refractive power between the forward negative lens system (L L and the backward positive lens system (L L L giving a negative power to an air lens provided between the third lens element (L and the fourth lens element (L and satisfying the above four conditions l) to (4). In the wide angle camera lens of retrofocus type according to the present invention, various aberrations, particularly the astigmatism and the coma can be highly compensated even though the refractive power of the negative lens system of the forward lens system is rather small, which is about from 0.9 f to 1.5 f and moreover there can be obtained a large amount of light at the periphery.

Now the meanings of the above four conditions (1) to (4) will be explained in detail hereinafter.

The first condition (1) is needed to keep the diameter of the front lens (L,) small. Moreover, if (t +t +t,)/(d +d becomes larger than 0.8, even though it is advantageous to keep the back focus long, but a position of an entrance pupil is far from the front surface of the first lens element (L so that the" curvature of the astigmatism is caused to be large by the forward lens system (L L The second condition (2) is necessary to compensate the spherical aberration and the distortion produced at the forward lens system (L,, L,). If d -l-d becomes smaller than 0.4 f, a distance between the forward neg ative lens system (L,, L,) and the master lens system (L L L becomes too small and therefore the refractive power of the forward lens system (L,, L must be increased, so that the coma and the distortion are deteriorated and it is quite difficult to compensate the coma and the distortion by means of the master lens system (L L L If d +d is chosen to be larger than 1.1 f, it is advantageous for compensating various aberrations, but the diameter of the first lens (L,) and the axial length of the whole lens system become large and this is very inconvenient for users.

The third condition (3) is necessary to obtain a long back focus without both increasing the negative refractive power of the forward lens system (L,, L,) and increasing the distance between the forward lens system (L,, L...) and the master lens system (L 1..., L This condition (3) is further advantageous tocompensate the astigmatism without deteriorating the coma aberration. lf r /r, is made smaller than 1.2, the negative power of the air lens becomes weakened and the back focus becomes small. In this case, in order to keep the back focus long, it is necessary to increase the negative power of the forward lens system (L,, L,) too much so that the coma and the spherical aberration become worse. For increasing the negative power of the air lens with keeping rJr, smaller than 1.2, it is necessary to make large a difference between refractive indices of the lens elements L and L, of the master lens system.

However, if the index of the front lens (L of the master lens system will be made small, a Petzval sum becomes deteriorated. If r lr, becomes larger than 3.5, it is favorable to keep the back focus long, howeverthe astigmatism becomes worse and the coma aberration becomes worse and it becomes quite difficult to compensate said astigmatism by means of the master lens system (L L L The fourth condition (4) is effective to compensate the coma aberration which is not fully corrected by the forward lens system (L L with maintaining the astigmatism in good status. If 2 becomes larger than 0.3 f, it will be very difficult to compensate satisfactorily the coma aberration up to the angle of field near 29 with keeping the symmetry of the coma aberration. In an embodiment of the present invention, a stop is arranged in the air space 2 so that only t, can be made small. This is favorable to compensate the chromatic aberration of magnification and the distortion.

A compact wide angle camera lens system according to a further aspect of the present invention satisfies the following two conditions (5) and (6) in addition to the above four conditions (1) to (4);

DESCRIPTION OF PREFERRED EMBODIMENT In FIGS. 1, 4 and 6, reference characters L L designate the different lens elements, r r designate the radii of curvature of the lens surfaces, d d

This fifth condition (5) is effective to limit the axial length of the wide angle lens system of retrofocus type. The upper limit 1 f in the condition (5) is needed to make the axial length smaller than about 1.5 f. This is accomplished by satisfying the sixth condition (6). The

rear lens surface of the third lens element (L and the front lens surface of the fourth lens element (L constitute the air lens having the negative power. Since the rear lens surface of this air lens has a larger divergency than the front lens surface of the air lens, by making the axial length d of the lens element (L in the master lens system (L L L larger than 0.7 times of the axial length d of the front lens element (L in the master lens system (L L L as defined in the condition (6), itis possible to keep the distance d +d short and maintain the back focus long without increasing r /r i.e. without affecting the astigmatism. If t,+d +t +d,+t becomes smaller than 0.6 f, in order to maintain the back focus long, r lr has to be increased or the negative power of the forward lens system has to be increased even if d, is made sufficiently larger than 0.7 d so that the coma and distortion become worse.

BRIEF DESCRIPTION OF THE DRAWINGS Now three embodiments of the wide angle camera lens system of retrofocus type according to the present invention will be described with reference to the ac- FIGS. 2A, 2B, 2C and 2D show different aberration curves of the wide angle lens system of the first embodiment;

I FIG. 3 shows curves illustrating the aperture efficiency of the first embodiment;

. designate the axial lengths of the lens elements and t t designate the air spaces provided between two adjacent lens surfaces.

EMBODIMENT I Numerical values of this first embodiment are given in the following Table I.

TABLE I Composite focal length f=l00 mm Relative aperture F 3.5

Seidel aberration characteristics of this first embodiment are given in the following Table II. In this Table II, a first column I shows the spherical aberration of each lens surface and their sum, a second column 11 shows the coma aberration of each lens surface and their sum, a third column 111 shows the astigmatism of each lens surface and their sum, a fourth column IV shows the distortion of each lens surface and their sum and finally a fifth column P shows Petzval sum of each lens surface and their sum.

TABLE II I II III IV P 1. 0.0000 0.01 16 0.0006 0.6021 0.0207 2 0.0024 0.0959 0.0151 0.8218 0.0337 3 0.1678 0.0356 0.0773 0.1995 0.3975 4 -10.3423 -0.5966 2.4840 0.3726 0.9547 5 0.7005 0.1415 0.3148 0.1055 0.0934

FIGS. 2A, 2B, 2C and 2D show curves illustrating the various aberrations. A solid curve in FIG. 2A represents the spherical aberration and a dotted curve in FIG. 2A shows the sine condition. In FIG. 2B, the solid curve, the dotted curve, the chain curve and the broken curve illustrate the chromatic aberrations for d-line, c line, F-line and g-line, respectively. FIG. 2C illustrates the distortion. In FIG. 2D, solid curve and dotted curve represent the Sagital astigmatism and the Meridional astigmatism, respectively.

FIG. 3 shows curves representing the aperture efficiency of the first embodiment for F 3.5 and F 5.6, respectively.

EMBODIMENT 2 TABLE III Composite focal length f 100 mm Relative aperture F 3.5

The Seidal aberration characteristics are given in the following Table IV.

TABLE IV I II III IV P 1 0.0000 0.0095 0.0004 0.6688 0.0152 2 0.0072 0.1344 0.03 l 2 0.B822 0.0702 3 0.0437 0.0467 0.0451 0.3313 0.2738 4 -l1.8974 -0.5767 2.6194 0.3291 0.9l83 5 1.8756 0.0969 0.4264 0.0595 0.1648 6 0.1934 0.1556 0.l735 0.3520 0.2367 7 l .4884 0.4063 0.7777 0.4817 0.5l56 8 8.2825 0.6775 2.3689 0.3636 0.5939 9 5.8293 0.2034 1.0888 0.1725 0.7202 10 0.0037 0.3404 0.0356 -0.3036 0.3721 11 4.2828 0.6280 1.6400 0.2974 0.1485 12 7.8879 0.8312 2.5605 0.48l8 --0.6529 13 0.7055 0.4075 0.5362 0.4306 0.1591 14 9.9351 0.4050 2.0060 0. l 829 0.5008 2 1.3196 0.0156 0.0295 0.2049 0.0969

The various aberration curves of the second embodi ment are shown in FIGS. 5A, 5B, 5C and 5D.

EMBODIMENT 3 FIG. 6 shows diagrammatically a third embodiment according to the invention. This third embodiment satisfies the above mentioned conditions (1) to (6), whereas the above first and second embodiments satisfy the conditions l to (4). The numerical data of the third embodiment are given in the following Table V.

Table V Composite focal length f mm The Seidel aberration characteristics are also given in the following Table VI. The various aberration curves are illustrated in FIGS. 7A, 7B, 7C and 7D. In FIGS. 8A, 8B and 8C, the aberration curves showing the spherical aberration and chromatic aberration, the astigmatism and the distortion, respectively are illustrated for the third embodiment with a magnification of l/40.

FIG. 9 shows the aperture efficiency of the third embodiment for F 3.5 and F 8, respectively.

I Table VI 1 11 1n 1v P 1 0.0000 0.0131 0.0008 0.6018 0.0234 2 0.0035 0.1088 0.0195 0.8224 0.0384 3 0.3873 0.0306 0.1088 0.1533 0.5151 4 12.7804 4.4685 2.4469 0.0964 1.0795 5 0.3915 0.2471 0.3110 0.2159 0.0246 6 0.1259 0.1642 0.1438 0.5152 0.28611 7 -1.3884 0.5048 0.8372 0.6538 0.5795 8 4,9655 0.5419 -1.6403 0.3705 0.57911 9 2.5296 0.2156 0.7385 0.2344 0.5875 10 0.2036 0.4219 -0.2965 0.3403 0.1983 11 4.2048 0.6124 1.6047 0.3145 0.2116 12 4.5883 0.7636 -1.8779 0.5341 0.5362 13 0.1280 0.2920 0.1933 0.4411 0 14 15.621 0.3044 2.1807 0.1355 0.6663 2 1.394 0.0047 0.0824 0.1932 0.1166

As can be seen from the above aberration character istics and the aperture efficiency, the wide angle camera lens systems of retrofocus type according to the present invention, the different aberrations are highly corrected and the aperture efficiency is also high. Moreover, the whole axial length of the lens system is very small, i.e. about l.35 f, which is very short as compared with known lens system of retrofocus type.

What I claimed is:

l. A wide angle camera lens system of retrofocus type consisting of a first lens (L consisting of a positive lens element having a small refractive power, a second lens (L consisting ofa negative meniscus lens element having a convex surface faced towards an object, a third lens (L consisting of a positive lens element, a fourth lens (L consisting of a positive meniscus lens element having a concave surface faced towards an object, a fifth lens (L consisting of a positive meniscus lens element, a sixth lens (L consisting of a biconcave negative lens element and a seventh lens (L consisting of a biconvex positive lens element and satisfies the following conditions;

t +t O.3f

wherein f designates a composite focal length 1,, t t designate air spaces formed between two adjacent lens elements, d d d, designate axial thicknesses of the lens elements, and r r r designate radii of curvature of the lens surfaces. 2. A wide angle camera lens system of retrofocus type as claimed in claim 1, said lens system further satisfies the following conditions;

3. A wide angle camera lens system of retrofocus type comprising a first lens (L consisting of a positive lens element having a small refractive power, a second lens (L consisting ofa negative meniscus lens element having a convex surface faced towards an object, a third lens (L consisting of a positive lens element, a fourth lens (L consisting of a positive meniscus lens element having a concave surface faced towards an object, a fifth lens (L consisting of a positive meniscus lens element, a sixth lens (L,) consisting of a biconcave negative lens element and a seventh lens (L consisting of a biconvex positive lens element, wherein f designates a composite focal length,

t,, t, t designate air spaces provided between two adjacent lens elements,

d d d, designate axial thicknesses of the lens elements, and

r,, r r designate radii of curvature of the lens surfaces,

said lens system satisfies the following numerical values;

4. A wide angle camera lens system of retrofocus type comprising a first lens (L consisting of a positive lens element having a small refractive power, a second lens (L consisting of a negative meniscus lens element having a convex surface faced towards an object, a third lens (L consisting of a positive lens element, a fourth lens (L consisting of a positive meniscus lens element having a concave surface faced towards an object, a fifth lens (L consisting of a positive meniscus lens element, a sixth lens (L consisting of a biconcave negative lens element and a seventh lens (L consisting of a biconvex positive lens element, wherein f designates a composite focal length, t t t designate air spaces provided between two adjacent lens elements, d d d designate axial thicknesses of the lens elements, and r r r designate radii of curvature of the lens surfaces, said lens system satisfies the following numerical values;

5. A wide angle camera lens system of retrofocus type comprising a first lens (L consisting of a positive 9 10 lens element having a small refractive power, a second L Thickens nesses lens (L consisting of a negative meniscus lens element cw Rad in mm and air Refractive Dispmive having a convex surface faced towards an ob ect, a ment spaces indices indices third lens (L consisting of a positive lens element, a l 712 07 mm r fourth lens 1 consisting of a positive meniscus lens 5 LI (11:10 n1=L66672 F4832 element havmg a concave surface faced towards an obr,=l,O4333 n=0.7l ject, a fifth lens (L consisting of a positive meniscus L 9 lens element, a sixth lens (L consisting of a biconcave r535 3 "P162041 F6027 negative lens element and a seventh lens (L-,) consistr,=l,63|.6l ing of a positive lens element, wherein 10 39 83 ig- "F "F4498 f designates a composite focal length, is t t t designate air spaces provided between two L, d =3l.29 n.=1.6779 v.=55.33

adjacent lens elements, "382 -5 d d d designate axial thicknesses of the lens ele- La 713 F5398 ments, and 15 r,.,=209.9s i,=|o.36 r r desi nate radii fcurv ure th s 2 g 0 at of e L. d,=6.93 1.74077 v,=27.79 I Surfaces r,,=79.4 3.04 said lens system satisfies the following numerical valr,,= L-, d =8.04 n =l.7l3 v =53.98

f 100 mm 2 

1. A wide angle camera lens system of retrofocus type consisting of a first lens (L1) consisting of a positive lens element having a small refractive power, a second lens (L2) consisting of a negative meniscus lens element having a convex surface faced towards an object, a third lens (L3) consisting of a positive lens element, a fourth lens (L4) consisting of a positive meniscus lens element having a concave surface faced towards an object, a fifth lens (L5) consisting of a positive meniscus lens element, a sixth lens (L6) consisting of a biconcave negative lens element and a seventh lens (L7) consisting of a biconvex positive lens element and satisfies the following conditions; (t2+t3+t4)/(d3+d4) <0.8 (1) 0.4f<d3+d4<1.1f (2) 1.2<<r6/r7<3.5, r6<0, r7<0 (3) t5+t6<0.3f (4) wherein f designates a composite focal length t1, t2 . . . t6 designate air spaces formed between two adjacent lens elements, d1, d2 . . . d7 designate axial thicknesses of the lens elements, and r1r2 . . . r14 designate radii of curvature of the lens surfaces.
 2. A wide angle camera lens system of retrofocus type as claimed in claim 1, said lens system further satisfies the following conditions; 0.6f<t2+d3+t3+d4+t4<1f (5) d4<0.7d3. (6)
 3. A wide angle camera lens system of retrofocus type comprising a first lens (L1) consisting of a positive lens element having a small refractive power, a second lens (L2) consisting of a negative meniscus lens element having a convex surface faced towards an object, a third lens (L3) consisting of a positive lens element, a fourth lens (L4) consisting of a positive meniscus lens element having a concave surface faced towards an object, a fifth lens (L5) consisting of a positive meniscus lens element, a sixth lens (L6) consisting of a biconcave negative lens element and a seventh lens (L7) consisting of a biconvex positive lens element, wherein f designates a composite focal length, t1, t2 . . . t6 designate air spaces provided between two adjacent lens elements, d1, d2 . . . d7 designate axial thicknesses of the lens elements, and r1, r2 . . . r14 designate radii of curvature of the lens surfaces, said lens system satisfies the following numerical values; f 100 mm Thick- Lens nesses ele- Radii in mm and air Refractive Dispersive ment spaces indices indices in mm r2 1,931,008 L1 d1 10.04 n1 1.66672 Nu 1 48.3 r3 -1,186.038 t1 0.71 r3 96.327 L2 d2 5.89 n2 1.62041 Nu 2 60.2 r4 40.104 t2 25.58 r5 364.602 L3 d3 47.27 n3 1.51633 Nu 3 64.0 r6 -207.110 t3 2.50 r8 -85.752 L4 d4 27.76 n4 1.71300 Nu 4 53.9 r8 -71.029 t4 0.71 r9 58.017 L5 d5 10.11 n5 1.66672 Nu 5 48.3 r10 123.080 t5 10.36 r11 -166.131 L6 d6 3.11 n6 1.71736 Nu 6 29.5 r12 70.417 t6 2.32 r13 256.417 L7 d7 8.04 n7 1.71300 Nu 7 53.9 r14 -73.019
 4. A wide angle camera lens system of retrofocus type comprising a first lens (L1) consisting of a positive lens element having a small refractive power, a second lens (L2) consisting of a negative meniscus lens element having a convex surface faced towards an object, a third lens (L3) consisting of a positive lens element, a fourth lens (L4) consisting of a positive meniscus lens element having a concave surface faced towards an object, a fifth lens (L5) consisting of a positive meniscus lens element, a sixth lens (L6) consisting of a biconcave negative lens element and a seventh lens (L7) consisting of a biconvex positive lens element, wherein f designates a composite focal length, t1, t2 . . . t6 designate air spaces provided between two adjacent lens elements, d1, d2 . . . d7 designate axial thicknesses of the lens elements, and r1, r2 . . . r14 designate radii of curvature of the lens surfaces, said lens system satisfies the following numerical values; f 100 mm Thick- Lens nesses ele- Radii in mm and air Refractive Dispersive ment spaces indices indices in mm r1 -2,646.190 L1 d1 10.04 n1 1.66998 Nu 1 39.3 r2 -571.864 t1 0.71 r3 139.839 L2 d2 5.89 n2 1.62041 Nu 2 60.2 r4 41.696 t2 27.36 r5 206.589 L3 d3 49.54 n3 1.51633 Nu 3 64.0 r6 -143.846 t3 2.50 r7 -80.732 L4 d4 23.54 n4 1.71300 Nu 4 53.9 r8 -70.086 t4 0.71 r9 55.707 L5 d5 10.04 n5 1.67000 Nu 5 51.6 r10 107.814 t5 10.36 r11 -281.225 L6 d6 3.11 n6 1.71736 Nu 6 29.5 r12 63.979 t6 2.5 r13 261.561 L7 d7 7.86 n7 1.71300 Nu 7 53.9 r14 -83.114
 5. A wide angle camera lens system of retrofocus type comprising a first lens (L1) consisting of a positive lens element having a small refractive power, a second lens (L2) consisting of a negative meniscus lens element having a convex surface faced towards an object, a third lens (L3) consisting of a positive lens element, a fourth lens (L4) consisting of a positive meniscus lens element having a concave surface faced towards an object, a fifth lens (L5) consisting of a positive meniscus lens element, a sixth lens (L6) consisting of a biconcAve negative lens element and a seventh lens (L7) consisting of a positive lens element, wherein f designates a composite focal length, t1, t2 . . . t6 designate air spaces provided between two adjacent lens elements, d1, d2 . . . d7 designate axial thicknesses of the lens elements, and r1, r2 . . . r14 designate radii of curvature of the lens surfaces, said lens system satisfies the following numerical values; f 100 mm Thick- Lens nesses ele- Radii in mm and air Refractive Dispersive ment spaces indices indices in mm r1 1,712.07 L1 d1 10.04 n1 1.66672 Nu 1 48.32 r2 -1,043.33 t1 0.71 r3 74.37 L2 d2 5.89 n2 1.62041 Nu 2 60.27 r4 35.49 t2 27.18 r5 1,631.61 L3 d3 22.61 n3 1.66892 Nu 3 44.98 r6 -139.83 t3 2.5 r7 -69.76 L4 d4 31.29 n4 1.6779 Nu 4 55.33 r8 -69.72 t4 0.71 r9 70.88 L5 d5 6.54 n5 1.713 Nu 5 53.98 r10 209.98 t5 10.36 r11 -201.19 L6 d6 6.93 n6 1.74077 Nu 6 27.79 r12 79.4 t6 3.04 r13 Infinity L7 d7 8.04 n7 1.713 Nu 7 53.98 r14 -62.5 